A team of scientists at Cornell University in Ithaca, N.Y., and the University of Queensland in Brisbane, Australia, have been trying for a number of years to figure out the role genes play in mate selection.

Of course, they would prefer to study the same thing in humans, but there seems to be an ethical problem with having people mate with strangers to produce children for scientific research.

So for now, fruit flies will have to do. These amazing creatures share many genes with higher life forms, including humans, and they go through so many generations in such a short period of time that they are very useful for research. And they're cheap, fortunately, because their lifespan is only a couple of weeks.

In their latest experiment, the researchers used two different strains of fruit flies that have lived in separate and controlled environments in their lab for 15 years.

Even Genes Can Choose Mr. Wrong

Would the flies from one strain prefer to mate with members of the other strain, instead of their closer kin, which can lead to all sorts of genetic problems? And would genes play a role in their decision?

"All the genes that the male had and all the genes that the female had somehow worked together in order to create the reproductive traits that ultimately happened during mating," said Lisa A. McGraw, the lead author of a study in the current issue of the journal Genetics.

She said it's clear that genes were the dominant factor, partly because "all of the females seemed to prefer one strain of males." Oddly enough, the strain they preferred turned out not to be the most successful males for procreation.

So their genes may have picked their mates, but the girls ended up with the wrong guys, reproductively speaking.

"It's not what you would predict," McGraw said.

Nice Guys Finish Last

For their experiment, the scientists picked a bunch of "virgin" flies from each strain, and each male was treated with a microscopic droplet of dye for later identification, blue for one strain and red for the other. Males and females from both strains were put in a "small mating chamber" made of clear plastic, affording the researchers a front-row view of the action.

All their genes must have been at work, because the girls overwhelmingly wanted the guys from one strain, and pretty much ignored the other strain. But the relatively few females that ended up with the rejected males "laid significantly more eggs" and produced more progeny, according to the study, so the best guys were chosen last.

"That's not a directionality that you would predict," McGraw said, because genes are supposed to facilitate finding the best mate for procreation of the species.